Turbochargers with waste gate valves have previously been described. A turbocharger serves to increase the boost pressure and thereby the power of the internal combustion engine. The pressure that can be generated is always a function of the exhaust gas quantity conveyed because the turbine wheel is coupled with the compressor wheel. It is therefore necessary to reduce or control the drive power acting on the compressor under certain operating conditions.
Waste gate valves, among others, are used to achieve this, the waste gas valves being arranged in a bypass channel by which the turbine can be bypassed so that the turbine wheel is no longer acted upon by the entire flow quantity of the exhaust gas. These waste gate valves are most often designed as flap valves operated by a pneumatic actuator which drives a linkage coupled with the flap.
Since a high thermal load exists in the region of the turbine housing due to the hot exhaust gases, these pneumatic actuators have been arranged in the region of the compressor, and in particular at a distance from the turbine housing, in order to reduce thermal load.
An exact control of the exhaust gas quantity discharged via the bypass channel is, however, difficult to achieve with a pneumatic actuator. Electric motors have therefore seen widespread use as drives for waste gate valves in recent years. These were typically also arranged at a distance from the turbine housing to reduce thermal load so that linkages were still used for coupling with the flap.
An actuator of a waste gate valve is described in DE 10 2011 002 627 A1 whose electric motor is arranged coaxially to an output shaft on which a lever is mounted via which a linkage is operated, the linkage being operatively connected with a waste gate flap arranged in the turbine housing. To avoid an overheating of the actuator, the waste gas valve is positioned on the compressor housing in the region of the fresh air inlet duct to obtain a thermal coupling therewith.
Due to ever decreasing available installation space, it is desirable to arrange the actuators of the waste gate valves in the immediate proximity to the valve itself since the installation space necessary is thus reduced and a more precise control becomes possible. When linkages are used, an increased wear of the mechanical components, in particular due to increased transverse forces in the region of the flap bearings, as well as increased assembly efforts, often further occur.
WO 2012/089459 A1 therefore describes a turbocharger with a water-cooled turbine housing and an integrated electric waste gate valve. The housing in which the electric motor for driving the waste gate valve and the transmission are arranged is a part of the turbine housing in which corresponding cooling ducts are formed to carry water. The electric motor and the transmission are thus mounted on the turbine housing, wherein the necessary opening in the turbine housing is closed with a cover. The bearing of the valve is also arranged in the turbine housing.
A risk of a thermal overload of the actuator still exists when the proposed arrangement of the waste gate valve is used since the cooling medium is strongly heated while flowing through the turbine housing and is not effective immediately at the actuator. The actuator is also subjected to a direct thermal radiation from outside so that, under unfavorable conditions, a risk of overheating still exists.